hwmon: (ds1621) Add ds1721 chip support

Update the ds1621 documentation, driver, and Kconfig with
ds1721 chip support.

Signed-off-by: Robert Coulson <rob.coulson@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 0428e8a..0114ed4 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -348,11 +348,14 @@
 	  will be called ds620.
 
 config SENSORS_DS1621
-	tristate "Dallas Semiconductor DS1621 and DS1625"
+	tristate "Dallas Semiconductor DS1621 and compatibles"
 	depends on I2C
 	help
-	  If you say yes here you get support for Dallas Semiconductor
-	  DS1621 and DS1625 sensor chips.
+	  If you say yes here you get support for Dallas Semiconductor/Maxim
+	  Integrated DS1621 sensor chips and compatible models including:
+
+	  - Dallas Semiconductor DS1625
+	  - Maxim Integrated DS1721
 
 	  This driver can also be built as a module.  If so, the module
 	  will be called ds1621.